<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="./jquery3.3.1.js"></script>
</head>
<body>
    <form id="formaa">
        <input type="text" name="user" class="user" value="你好">
        <input type="password" name="pass" class="pass" value="123456">
    </form>
    <script>
        $(function(){
            // obj.value以前
            //通过val()读取value的值
            // alert($(".pass").val())

            // 设置
            $(".user").val("我好啊 我很好")
        })
    </script>
</body>
</html>